Clinical Nuclear Medicine

Tomography

A picture of a slice, imaging technique that creates detailed 3D, sectional, or "slice-by-slice" views of an object

Tomography Images

2D (Planar/Projection) --> Semiqualitative

3D (Tomogram) --> Qualitative

Sinogram

Transform of projection data, 2D representation of tomographic X-ray or PET data

SPECT Projection

Image @60-90 degrees for 20-40 seconds

PET/CT sensitivity vs SPECT

PET/CT Sensitivity = 100-1000x SPECT

Scintillation Detectors

Convert absorbed radiation into pulses of light

Ionization Chambers

Gas filled chambers that detect ion pairs

ROC Curve

Assesses the overall diagnostic performance of a test

Inverse Square Law

Intensity if inversely proportional to the square of the distance

Deadtime

Time for a detector to process an event

Dose Calibrator QC

Accuracy (Daily), Constancy (Daily), Geometry (At installation), Linearity (Quaterly)

How Scintillator works

Uses a PMT to amplify light signal using dynodes

Photopeak Energy Used

20%

Intrinsic

Without collimation

Extrinsic

With collimation

Useful FOV

Crystal area

CFOV

Inner 75% of crystal area (Clinical imaging area)

Gamma Camera Collimation types

Parallel hole, Diverging, Converging, Pinhole

Anger logic

used to determine the x,y position of an event

Gamma Camera QC

Energy resolution, Count rate performance, Uniformity, Sensitivity, Spatial resolution, Constancy, Multipeak registration

Flood field nonuniformity

Mistuning, uncoupled PMT, cracked crystal, crystal hydration, outdated correction tables

Gamma camera collimator does

directionalizes radiation by only letting perpendicular radiation to reach the crystal

________ resolution dominates __________ resolution

collimator, system

SPECT reconstruction algorithms

Filtered back projection (Analytic, fast), Iterative reconstruction (serial guesses, slow, better quality)

Fourier transform

expression of an image as a sum of sin waves

Nyquist frequency

Maximum spatial frequency

PET Positron negatron annhilation

To antiparallel 511 kev gamma photons are created

Coincidence detection

2 events received within the same timing window

2D PET perk

minimize scatter

3D PET perk

Maximum sensitivity

Time of flight PET

determine the location between two detectors at which annihilation occurs based on delta t

PET Corrections

Decay, Deadtime, randoms, normalization, scatter and annhilation

Pregnant woman risk

50% increase in childhood caner per RAD, no risk fo birth defects at diagnostic levels

MIRD

used to calculate absorbed dose from internally administer radiopharm. each organ is a source and target

In filtered back projection reconstruction of SPECT images

as the cut-off frequency Vc is reduced, the images become "smoother" (less noisy) but at the cost of poorer spatial resolution